Dielectric porcelain composition, multilayer ceramic capacitor, and electronic component

ABSTRACT

A dielectric ceramic composition of the present invention includes 100 parts by mole of BaTiO 3 , x 1  parts by mole of MnO, x 2  parts by mole of Cr 2 O 3 , x 3  parts by mole of Y 2 O 3  and/or Ho 2 O 3 , x 4  parts by mole of oxide selected from the group consisting of BaO, CaO and SrO, and x 5  parts by mole of SiO 2  and/or GeO 2 , where 0.5≦x 1 ≦4.5, 0.05≦x 2 ≦1.0, x 1 +x 2 ≦4.55, 0.25≦x 3 ≦1.5, 0.5 ≦x 4 ≦6 and 0.5≦x 5 ≦6. A multilayer ceramic capacitor of the present invention includes a laminated structure of a ceramic dielectric made of such a composition and an electrode made of Ni or Ni alloy.

TECHNICAL FIELD

The present invention relates to a dielectric ceramic composition whichis usable as a dielectric material of a capacitor. The invention alsorelates to a multilayer ceramic capacitor, and an electronic componentincluding a portion made of such a dielectric material.

BACKGROUND ART

A multilayer ceramic capacitor which utilizes, as the dielectricmaterial between electrodes, a ceramic composition containing titanatesuch as barium titanate as the main component is one of essential partsfor recent electronic devices for industrial or consumer use, becausesuch a capacitor can have a small size and a large capacitance,excellent electric characteristics for a wide frequency band and goodheat resistance, and can be easily mass-produced.

To manufacture such a multilayer ceramic capacitor, an organic binder, aplasticizer, a solvent and a dispersant, for example, are added andmixed with the BaTiO₃-based material powder of a ceramic composition toprepare slurry. Subsequently, by a doctor blade method, for example, agreen sheet of the dielectric ceramic composition is prepared from theslurry. Then, conductive paste including metal powder for forming aninner electrode is printed on the green sheet. A plurality of greensheets formed in this way and each having conductive paste printed onthe obverse surface are so laminated that the conductive paste and thegreen sheet are alternately positioned and bonded under pressure.Subsequently, the laminated product is baked at a predetermined bakingtemperature to be integral (baking step). In the baking step, theceramic composition in each green sheet sinters to form a ceramicdielectric layer, and metal powder in the conductive paste sinters toform inner electrodes. Thereafter, a pair of outer electrodes, each ofwhich is electrically connected to a predetermined group of innerelectrodes, are formed on surfaces of the laminated product.

In the above-described baking process, for the BaTiO₃-based ceramiccomposition to properly sinter and exhibit good dielectriccharacteristics in the multilayer ceramic capacitor, the ceramiccomposition needs to be baked at high temperatures of about 1150-1350°C. On the other hand, as the metal for forming the inner electrodes, ametal material needs to be used which has a melting point that is higherthan the baking temperature of the baking process, which can be baked atthe same baking temperature as the ceramic composition, and which is notsubstantially oxidized at the high temperature in the baking process. Asthe metal materials that satisfy such conditions, Pd, Pt or alloysthereof are known. However, these metal materials are expensive, andhence, are not preferable. When such metal materials are used as theinner electrode material, the cost for the electrode materialunfavorably increases as a larger number of layers are stacked toincrease the capacitance of the multilayer ceramic capacitor.

Therefore, as the inner electrode material, the use of Ni and Ni alloyshave been considered that are relatively inexpensive, have a lowspecific resistance and a melting point higher than the sinteringtemperature of the BaTiO₃-based ceramic composition, and can be baked atthe same temperature as the ceramic composition. However, in the bakingat high temperatures in an atmosphere containing oxygen, i.e., in theair, for example, Ni isoxidized and the function as the electrode maybelost. Further, nickel oxide maybe taken into the ceramic composition todeteriorate the properties of the capacitor.

When the baking step is performed in a reducing atmosphere or alow-oxygen atmosphere to prevent the oxidation of Ni, the BaTiO₃-basedceramic composition is reduced to change the valence of Ti from 4 to 3.As a result, the composition becomes a semiconductor, and the insulatingproperty is deteriorated. Further, the baking step in a reducingatmosphere or a low-oxygen atmosphere increases the oxygen vacancy inthe BaTiO₃-based ceramic composition, so that the life of the ceramiccomposition (time before insulation deterioration occurs) tends to beshortened.

Therefore, as a reduction-resistant BaTiO₃-based ceramic composition inwhich properties deterioration such as a decrease in insulationresistance is less likely to occur even in the baking in a reducingatmosphere, a composition in which the molar ratio of BaO/TiO₂ is noless than 1 or a composition in which part of Ba is replaced by Ca havebeen developed. Such ceramic compositions are disclosed inJP-A-S55-67567, for example.

On the other hand, due to the development of electronic devices having asmall size, multifunction and high performance, a small size and a largecapacitance are demanded for a capacitor which constitutes an electriccircuit to be incorporated in such electronic devices. To satisfy thedemand, in addition to the improvement of the dielectric material, thethickness of the dielectric layer between electrodes tends to be reducedto enable the lamination of a larger number of layers. However, toproperly reduce the thickness of the dielectric layer, the ceramiccomposition constituting the dielectric layer needs to have a sufficientinsulation resistance, and the deterioration with time of the ceramiccomposition needs to be sufficiently small. Further, in accordance withthe size reduction, increase of functions and improvement of performanceof an electronic device, its electric circuit has high density and islikely to be heated up during the use of the device. Therefore, for theceramic composition constituting the dielectric layer of a capacitor inthe electric circuit, it is demanded more strongly than before that theproperties of the composition do not change largely due to thetemperature change.

Such enhancement of properties and reliability is also demanded withrespect to the reduction-resistant BaTiO₃-based ceramic composition, andthe enhancement of properties and reliability by adding various oxideshave been studied. For example, such ceramic composition is disclosed inthe Patent Documents 1-5 described below.

However, in prior art BaTiO₃-based ceramic composition, it is difficultto satisfactorily enhance the insulation resistance, suppress thedeterioration with time of the insulation resistance and suppress thecapacitance change relative to temperature change while ensuringsufficient reduction-resistance. Therefore, with the prior arttechnique, it is difficult to enhance the properties of a multilayerceramic capacitor utilizing Ni or Ni alloy as the inner electrodematerial to a level equal to or higher than that of a multilayer ceramiccapacitor having Pd inner electrodes.

Patent Document 1: JP-A-S61-36170

Patent Document 2: JP-A-H06-5460

Patent Document 3: JP-A-H06-342735

Patent Document 4: JP-A-H08-124785

Patent Document 5: JP-A-H09-171937

DISCLOSURE OF THE INVENTION

The present invention is conceived under the circumstances describedabove. It is, therefore, an object of the present invention to provide adielectric ceramic composition which has a high insulation resistanceeven after the baking in a reducing atmosphere, whose deterioration ofthe insulation resistance (IR) with time is small (i.e., the IRaccelerated life is long), whose capacitance change relative totemperature change is small and which is resistant to reduction, toprovide a multilayer ceramic capacitor utilizing the composition as thematerial for the dielectric layer between electrodes, and to provide anelectronic component including a portion made of the composition.

According to a first aspect of the present invention, a dielectricceramic composition is provided. The dielectric ceramic compositioncomprises 100 parts by mole of BaTiO₃, x₁ parts by mole of MnO, x₂ partsby mole of Cr₂O₃, x₃ parts by mole of Y₂O₃ and/or Ho₂O₃, x₄ parts bymole of oxide selected from the group consisting of BaO, CaO and SrO,and x₅ parts by mole of SiO₂ and/or GeO₂, where 0.5≦x₁≦4.5, 0.05≦x₂≦1.0,x₁+x₂≦4.55, 0.25≦x₃ ≦1.5, 0.5≦x ₄≦6 and 0.5≦x₅≦6.

Preferably, the dielectric ceramic composition according to the firstaspect of the present invention further comprises 0.01 to 1.0 part bymole of V₂O₅. Preferably, the dielectric ceramic composition accordingto the first aspect of the present invention further comprises 0.2 to1.0 part by mole of Al₂O₃ and/or B₂O₃.

According to a second aspect of the present invention, a multilayerceramic capacitor comprising a laminated structure of a ceramicdielectric and an electrode is provided. In the capacitor, the ceramicdielectric is made of a dielectric ceramic composition having any one ofthe structures described above as the first aspect of the presentinvention. The electrode is made of Ni or an alloy containing Ni.

According to a third aspect of the present invention, an electroniccomponent is provided. The electronic component includes a portion madeof the dielectric ceramic composition having any one of the structuresdescribed above as the first aspect of the present invention.

To solve the problems described before, the inventors of the presentinvention have performed various studies about the BaTiO₃-baseddielectric ceramic composition to enhance the properties. Specifically,the inventors repeated the operations of adding different kinds ofoxides to BaTiO₃ as the base material, baking the ceramic composition,and examining the properties to know how close the properties of thecomposition were to the intended properties. Although the action of thecomponents to be added have been known to some degree throughexperiences, and the reasons therefor have been explained in variousways, the properties cannot be confirmed without actually preparing theproduct (ceramic composition or an electronic component utilizing thecomposition) and examining the characteristics.

Therefore, on the condition that the ceramic composition can be sinteredinto a dense compact at temperatures up to 1350° C. in a reducingatmosphere and has a dielectric constant of 3000 or more at 1 kHz, theinfluences of the included components were examined, and compositionswhich can exceed the predetermined target values of the insulationresistance, the dielectric strength, the IR accelerated life and thetemperature dependence of capacitance (capacitance change relative totemperature change) were selected.

According to the study of the effect of adding MnO which is a componentto enhance the resistance to reduction, a higher content of MnO in theceramic composition provides a higher resistance to reduction in theceramic composition but also provides a larger capacitance changerelative to the temperature change. When MgO, for example, is added tothe ceramic composition to decrease the temperature dependence,disadvantages such as a decrease in relative dielectric constant and arise of the baking temperature necessary for proper sintering may becaused. When a sintering assistant such as LiO₂ or B₂O₃ is added, thebaking temperature can be lowered. In such a case, however, grain growthoccurs during the baking, and the capacitance change relative to thetemperature change increases. In this way, the addition of a certainkind of component by a certain amount to improve a certain propertyoften results in the deterioration of another property.

These studies have revealed that, in adding MnO and increasing theamount to enhance the resistance to reduction, the simultaneous additionof an appropriate amount of Cr₂O₃ can reduce the temperature dependenceof capacitance. Although the reason why the addition of MnO and Cr₂O₃ incombination provides such an effect is not clear, this method caneliminate the need for adding MgO, which is generally used to reduce thetemperature dependence. Since the addition of MgO raises the temperaturenecessary for sintering, the amount of a sintering assistant, whichtends to reduce the dielectric constant and the insulation resistance,need be increased to lower the sintering temperature. However, it isfound that, by controlling the total amount of MnO and Cr₂O₃, thecapacitance change relative to the temperature change and the rise ofthe sintering temperature can be suppressed without the need forincreasing the amount of the sintering assistant.

Therefore, the composition consisting of BaTiO₃ to which MnO and Cr₂O₃were added was determined as the base composition, and addition of othercomponents was studied to further enhance various properties. As aresult, it was confirmed that the addition of rare earth elements suchas Y₂O₃ and Ho₂O₃ enhanced the IR accelerated life (reliability).

However, the addition of oxides of the rare earth elements tends toraise the baking temperature necessary for providing a dense sinteredbody. Therefore, study was performed to find a sintering assistant whichcan lower the baking temperature without largely influencing otherproperties, and the addition Of MO₂ (“M” represents Si or Ge) incombination with AO (“A” represents Ba, Ca or Sr) was found to bepreferable. The combined use of at least one of BaO, CaO and SrO and atleast one of SiO₂ and GeO₂ had sufficient effect of lowering the bakingtemperature and enhancing the density of the sintered body. Thesesubstances form glass at grain boundaries and have the effect oflowering the sintering temperature efficiently even when used by a smallamount.

Further, it was found that the content of V₂O₅ by a small amount couldprolong the IR accelerated life and lower the sintering temperature, sothat it is preferable to add V₂O₅ as required. Further, at least one ofAl₂O₃ and B₂O₃ may be added, because these substances are effective forlowering the sintering temperature and improving the temperaturecharacteristics.

By using the dielectric ceramic composition obtained in this way andhaving a high insulation resistance, high dielectric strength and a longIR accelerated life, a multilayer ceramic chip capacitor was prepared byforming Ni inner electrodes and baking simultaneously in a reducingatmosphere. The properties as a dielectric was examined and found to beexcellent.

Since the intended properties were achieved in this way, the appropriateaddition amount of each component was studied specifically, whereby thepresent invention having the structures as described as the firstthrough the third aspects was completed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a multilayer ceramic capacitor.

FIG. 2 is a table showing the compositions (except for BaTiO₃) ofdielectric ceramic compositions of inventive examples 1-21 for formingthe dielectric layer of a multilayer ceramic capacitor.

FIG. 3 is a table showing the compositions (except for BaTiO₃) ofdielectric ceramic compositions of inventive examples 22-33 andcomparative examples 1-8 for forming the dielectric layer of amultilayer ceramic capacitor.

FIG. 4 is a table showing the results of the properties test carried outwith respect to the multilayer ceramic capacitors of inventive examples1-21.

FIG. 5 is a table showing the results of the properties test carried outwith respect to the multilayer ceramic capacitors of inventive examples22-33 and comparative examples 1-8.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a sectional view showing a multilayer ceramic capacitor 10 asan example of electronic component manufactured by using a dielectricceramic composition according to the present invention. The multilayerceramic capacitor 10 includes dielectric layers 11, a plurality of innerelectrodes 12, and a pair of outer electrodes 13. The dielectric layers11 are made of the ceramic composition of the present invention, andeach of the dielectric layers is arranged to partially intervene betweenthe inner electrodes 12. A predetermined set of inner electrodes 12 areelectrically connected to one of the outer electrodes 13, whereasanother set of inner electrodes 12 are electrically connected to theother outer electrode 13. The inner electrodes 12 are made of Ni or Nialloy, whereas the external electrodes 13 are made of Cu or Cu alloy.

The dielectric ceramic composition of the present invention containsBaTiO₃, MnO and Cr₂O₃. The composition further contains Y₂O₃ and/orHo₂O₃. The composition further contains an oxide selected from the groupconsisting of BaO, CaO and SrO and further contains SiO₂ and/or GeO₂.

MnO is contained to enhance the reduction resistance of the dielectricceramic composition (i.e., to suppress the decrease of the insulationresistance of the dielectric ceramic composition due to the baking in areducing atmosphere). When the content of MnO relative to 100 parts bymole of BaTiO₃ is expressed as x₁, x₁ is in the range of 0.5≦x₁≦4.5.When x₁ is lower than 0.5, the decrease of the insulation resistance maynot be prevented satisfactorily. When x₁ exceeds 4.5, the change ofcapacitance relative to the temperature change (temperature dependenceof capacitance) tends to become large.

Cr₂O₃ is contained to enhance the reduction resistance and to reduce thetemperature dependence of capacitance in the coexistence of MnO. Whenthe content of Cr₂O₃ relative to 100 parts by mole of BaTiO₃ isexpressed as x₂, x₂ is in the range of 0.05≦x₂≦1.0. When x₂ is lowerthan 0.05, the effects of the enhancement of the reduction resistanceand the suppression of the temperature dependence cannot be obtainedsufficiently. When x₂ exceeds 1.0, the temperature necessary forsintering the dielectric ceramic composition becomes high, and thedielectric ceramic composition may not properly sinter at temperaturesbelow the melting point of Ni.

When the total content of MnO and Cr₂O₃ is excessive, the temperaturedependence of capacitance becomes undesirably large. Therefore, x₁+x₂needs to be no more than 4.55.

Y₂O₃ and/or Ho₂O₃ is contained to prolong the IR accelerated life. Whenthe total content of Y₂O₃ and/or Ho₂O₃ relative to 100 parts by mole ofBaTiO₃ is expressed as x₃, x₃ is in the range of 0.25≦x₃≦1.5. When x₃islower than 0.25, the life cannot be prolonged sufficiently. When x₃exceeds 1.5, the baking temperature necessary for obtaining a densesintered body becomes undesirably high.

When an oxide (AO) selected from the group consisting of BaO, CaO andSrO and an oxide (MO₂) selected from the group consisting of SiO₂ andGeO₂ are contained in combination, the effects of a sintering assistantare obtained, i.e. glass is formed at grain boundaries in sintering theceramic composition, and the baking temperature for obtaining a densesintered body can be decreased to promote sintering. When the content ofAO relative to 100 parts by mole of BaTiO₃ is expressed as x₄, x₄ is inthe range of 0.5≦x₄≦6.0. When the content of MO₂ relative to 100 partsby mole of BaTiO₃ is expressed as x₅, x₅ is in the range of 0.5≦x₅≦6.0.When x₄ or x₅ is lower than 0.5, the effects as the sintering assistantcannot be obtained sufficiently. When x₄ or x₅ exceeds 6.0, a decreasein dielectric constant or an increase in temperature dependence ofcapacitance may be caused.

The dielectric ceramic composition of the present invention may containV₂O₅ to further prolong the IR accelerated life. In this case, when thecontent of V₂O₅ relative to 100 parts by mole of BaTiO₃ is expressed asx₆, x₆ is in the range of 0.01≦x₆≦1.0. When x₆ is lower than 0.25, theeffect of V₂O₅ to prolong the life cannot be obtained sufficiently. Whenx₆ exceeds 1.0, a decrease in dielectric constant or an increase intemperature dependence of capacitance may be caused.

The dielectric ceramic composition of the present invention may containAl₂O₃ and/or B₂O₃ to further lower the baking temperature necessary forsintering the dielectric ceramic composition and to provide a densesintered body. In this case, when the total content of Al₂O₃ and/or B₂O₃relative to 100 parts by mole of BaTiO₃ is expressed as x₇, x₇ is in therange of 0.2≦x₇≦1.0. When x₇ is lower than 0.5, the effect of Al₂O₃and/or B₂O₃ cannot be obtained sufficiently. When x₇ exceeds 1.0, anincrease in temperature dependence of capacitance may be caused.

The dielectric ceramic composition of the present invention, when itundergoes the baking at temperatures below e.g. 135° C. in a reducingatmosphere or a low-oxygen atmosphere, exhibits high insulationresistance and high dielectric strength, a sufficient life in anaccelerated test at high temperature and high voltage. Further, thechange of capacitance relative to the temperature change is small.

For instance, the dielectric ceramic composition of the presentinvention can exhibit dielectric constant of 3000 or more at 1 kHz,capacitance resistance product (CR product) of 2000 Ω·F or more at highvoltage (5 V/μm), dielectric strength of 70 V/μm or more, capacitancereduction of 30% or less upon DC application of 3 V/μm, life of one houror more before the insulation resistance decreases to 10⁵Ω or less (IRaccelerated life) upon the application of 30 V/μm at 200° C.

Further, in the dielectric ceramic composition according to the presentinvention, the temperature dependence of the capacitance can satisfy thecondition of the X7R characteristics of EIA standard (i.e., the changeof capacitance at −55 to 125° C. relative to the capacitance at thereference temperature of 25° C. is within ±15%), and further satisfy thecondition of the B characteristics of JIS (i.e., the change ofcapacitance at −25 to 85° C. relative to the capacitance at thereference temperature of 20° C. is within ±10%).

The above properties could not be obtained in a prior-art dielectricceramic composition for Ni inner electrodes and are equivalent orsuperior to the properties of the dielectric ceramic composition for Pdinner electrodes baked at high temperatures in an oxidizing atmosphere.

The multilayer ceramic capacitor 10 is manufactured as follows. First,BaTiO₃ powder which is the main component and oxides of Mn, Cr, Y, Ho, Vand the like are weighed and mixed to provide a prescribed compositionand pre-baked at 80 to 1200° C. for one to five hours. Subsequently, thepre-baked powder mixture is pulverized. To obtain excellent dielectriccharacteristics of the dielectric composition, it is preferable toperform the pulverization until the average particle size becomes 0.1 μmor less.

The components such as AO(BaO, CaO, SrO), MO₂ (SiO₂, GeO₂), Al₂O₃, B₂O₃,which are to become oxide glass, are heated to a high temperature formelting and then suddenly cooled and pulverized to produce oxide glasspowder.

Subsequently, glass powder, an organic binder, a plasticizer, a solventand a dispersant, for example, are added to and mixed with the pre-bakedpowder to prepare slurry. Then, by a doctor blade method, for example, agreen sheet of a predetermined thickness is prepared from the slurry.Then, conductive paste including metal powder for forming innerelectrodes is printed on the green sheet. A plurality of green sheetsformed in this way and each having an obverse surface on whichconductive paste is printed are laminated so that the conductive pasteand the green sheet are alternately positioned, and then bonded underpressure. Subsequently, the laminated product is subjected topretreatment heating for removing the binder, baking (baking step) at ahigh temperature of 1100 to 1350° C. for sintering and re-oxidationtreatment at a high temperature in a predetermined oxidizing atmosphere.If the baking step is performed at a baking temperature above 1350° C.,Ni or Ni alloy are likely to agglomerate and may be baked like anisland. Therefore, the baking temperature up to 1350° C. is preferable.

Subsequently, a pair of outer electrodes 13 as connection terminals toan external circuit are formed at predetermined positions of thelaminated body. The multilayer ceramic capacitor 10 can be manufacturedin the above-described manner, for example.

EXAMPLES AND COMPARATIVE EXAMPLES

[Preparation of Multilayer Ceramic Capacitor]

A plurality of multilayer ceramic capacitors which were different fromeach other in composition of the dielectric layer between electrodeswere prepared as capacitors of inventive examples 1-33 and thosecomparative examples 1-8. FIG. 2 shows the dielectric ceramiccompositions (except for BaTiO₃) constituting the dielectric layerbetween electrodes in the capacitors of the inventive examples 1-21.FIG. 3 shows the dielectric ceramic compositions (except for BaTiO₃)constituting the dielectric layer between electrodes in the capacitorsof the inventive examples 22-33 and the comparative examples 1-8. InFIGS. 2 and 3, the relative amount of substance of each oxide relativeto 100parts by mole of BaTiO₃is described.

The capacitors of inventive examples 1-33 and comparative examples 1-8were prepared as follows. First, BaTiO₃ powder (average particle size of0.4 μm) obtained by oxalate coprecipitation, MnO powder, Cr₂O₃ powder,V₂O₅powder, and Y₂O₃ powder and Ho₂O₃ powder if necessary, were weighedand mixed, and then pre-baked at 1100° C. for seven hours. Thereafter,the powder mixture was pulverized, whereby first oxide powder having anaverage particle size of up to 0.1 μm was obtained.

The appropriate one or ones of carbonates of Ba, Ca and Sr to obtain thefunction of a sintering assistant, and SiO₂ and/or Ge₂O₃, and Al₂O₃and/or B₂O₃ to obtain the function of a sintering assistant were weighedand mixed, and then pre-baked at 1250° C. for two hours. Thereafter, thepowder was pulverized, whereby second oxide powder having an averageparticle size of up to 0.1 μm was obtained.

By mixing the two kinds of oxide powders at a prescribed ratio, thematerial powder was obtained.

Next, 700 g of toluene-ethanol solvent containing a plasticizer and adispersant was added to 1000 g of material powder, and a dispersingprocess using a ball mill was performed for two hours to prepare slurryhaving a viscosity of about 200 cps. Thereafter, the slurry was appliedonto a PET film by using a lip-coater type applicator, whereby a greensheet having a thickness of 2.5 μm was prepared.

Subsequently, conductive paste containing Ni powder was printed on thegreen sheet to form an inner electrode pattern (thickness 1.5 μm). Inthis way, a plurality of green sheets each formed with an innerelectrode pattern thereon were prepared. After the PET film as the basemember was peeled off from each of the green sheets, the green sheetswere so laminated that the inner electrode pattern and the green sheetare alternately positioned (effective lamination number: 350) and heatedfor bonding under pressure.

Then, the laminated body was cut into a predetermined size to providegreen chips. Thereafter, the green chips were subjected to de-bindertreatment, i.e. heated at 400° C. for twelve hours in nitrogen gas.Subsequently, the green chips were subjected to a baking process(sintering process), i.e. heated at 1100 to 1350° C. for four hours in amixed gas of humidified nitrogen and hydrogen. In the baking-process,the ceramic composition in each of the green sheets was sintered to forma dielectric layer, and Ni powder in the conductive paste was sinteredto form an inner electrode. The baking temperature had been determinedin advance with respect to each kind of green chip and green sheet.Specifically, samples having the same structure as the green chips hadbeen prepared and baked at different baking temperatures to find thelowest baking temperature which could provide dense sintered bodies.

Then, the sintered laminated body, having undergone the baking process,was subjected to annealing by heating at 1000° C. in humidified nitrogenfor three hours.

Subsequently, after a predetermined end surface of the sinteredlaminated body was polished, conductive paste containing Cu powder wasapplied to the polished surface. Then, by heating at 850° C. in anitrogen atmosphere for two hours, the conductive paste was formed intoan outer electrode. In this way, the capacitors of inventive examples1-33 and those of comparative examples 1-8 were prepared. Each of thecapacitors had a length of 3.1 mm, a width of 1.6 mm and a thickness of1.6 mm. In each capacitor, the effective dielectric layer had athickness of 2.0 μm, and the inner electrode had a thickness of 1.2 μm.

[Performance Examination]

The capacitors of inventive examples 1-33 and those of comparativeexamples 1-8 were examined for the dielectric constant, the dielectricloss (tan δ), the CR product, the dielectric strength, the temperaturedependence of capacitance, the DC-Bias characteristics and the IRaccelerated life. The examination results are given in the tables ofFIGS. 4 and 5.

The dielectric constant and the dielectric loss (tan δ) were obtainedfrom the capacitance at 20° C., the electrode area and the thickness ofthe dielectric under the conditions of 1 V and 1.0 kHz.

To obtain the CR product, the one minute value of insulation resistancewhen 5V was applied per 1 μm thickness of dielectric at 25° C. wasmeasured. The measured value was multiplied by the capacitance to obtainthe CR product. The CR value serves as an indicator of the level of theinsulation resistance, and hence, serves as an indicator of thereduction resistance.

As to the dielectric strength, the voltage applied to the capacitors wascontinuously increased, and the voltage at which the current of 10 mA ormore flowed was measured using fifty sample capacitors for eachcomposition. The intermediate value of the fifty measured values of eachcapacitor is described in the table as the representative value.

As to the temperature dependence of the capacitance, whether thecapacitors satisfied the conditions of X7R characteristics of EIAstandard and “B” characteristics of JIS was examined. As to the X7Rcharacteristics of EIA standard, the capacitance at a measurementvoltage of 1V was measured at a plurality of points in the temperaturerange of −55 to 125° C. by using an LCR meter, and determination wasmade as to whether or not the change of capacitance relative to thecapacitance at the reference temperature of 25° C. was within ±15%. Asto the “B” characteristics of JIS, the capacitance at a measurementvoltage of 1V was measured at a plurality of points in the temperaturerange of −25 to 85° C. by using an LCR meter, and determination was madeas to whether or not the change of capacitance relative to thecapacitance at the reference temperature of 20° C. was within ±10%. Themark “∘” is applied to the capacitors which satisfied the aboveconditions, whereas the mark “×” is applied to the capacitors which didnot satisfy the above conditions.

As to the DC-Bias characteristics, the capacitance when DC voltage of 6Vand AC voltage of 1 Vrms and 1.0 kHz were applied in a superposingmanner was measured, and the decreasing ratio of the capacitancerelative to the capacitance when AC voltage of 1 Vrms and 1.0 kHz wasapplied was obtained. The DC-Bias characteristics serves as an indicatorof deterioration with time of the insulation resistance.

As to the IR accelerated life, DC voltage of 60 V (30 V/μm) was appliedat 200° C., and the time period before the insulation resistancedecreases to 10₅Ω or less was measured as the IR lifetime. The IRaccelerated life serves as an indicator of reliability.

[Evaluation]

As will be understood from the examination results given in the tablesof FIGS. 4 and 5, the dielectric ceramic composition of the presentinvention, which contains BaTiO₃, an appropriate amount of MnO and Cr₂O₃added thereto, Y₂O₃ and/or Ho₂O₃ further added thereto and glassformation comprising BaO, CaO, SrO or the like and SiO₂, GeO₂ or thelike, does not deteriorate the properties as the dielectric, is suitablefor the use of Ni or the like for the electrode and becomes a densesintered body at a baking temperature of 1150 to 1350° C. Even after thebaking step in a reducing temperature in the manufacturing process, thecapacitors made by using the dielectric ceramic composition of theinvention exhibit dielectric constant higher than 3000, CR producthigher than 2000, dielectric strength higher than 80V/μm, lowtemperature dependence of capacitance, and IR accelerated life of noless than 1.5 hour which indicates high reliability.

However, in a composition departing from the composition range of thepresent invention, i.e., in the capacitor of the comparative example 1in which the MnO content is too low, for example, the CR product is lowand the insulation resistance is insufficient. The capacitor of thecomparative example 3 in which the Cr₂O₃ content is too low and thecapacitor of the comparative example 5 in which the total content ofY₂O₃ and Ho₂O₃ is too low have a problem with the temperature dependenceof capacitance. The capacitor of the comparative example 8 in which theBaO content and the SiO₂ content are too high has a short IR acceleratedlife and hence has low reliability. Further, proper performanceexamination could not be performed with respect to the capacitor of thecomparative example 2 in which the MnO content was too high, thecapacitor of the comparative example 4 in which the Cr₂O₃ content wastoo high, the capacitor of the comparative example 6 in which the Y₂O₃content was too high, and the capacitor of the comparative example 7 inwhich the BaO content and the SiO₂ content were too low, because thecompositions could not be sintered properly at temperatures up to 1350°C.

1. A dielectric ceramic composition comprising 100 parts by mole ofBaTiO₃, x₁ parts by mole of MnO, x₂ parts by mole of Cr₂O₃, x₃ parts bymole of Y₂O₃ and/or Ho₂O₃, x₄ parts by mole of oxide selected from thegroup consisting of BaO, CaO and SrO, and x₅ parts by mole of SiO₂and/or GeO₂, wherein 0.5≦x₁≦4.5, 0.05≦x₂≦1.0, x₁+x₂≦4.55, 0.25≦x₃≦1.5,0.5≦x₄≦6 and 0.5≦x₅≦6.
 2. The dielectric ceramic composition accordingto claim 1, further comprising 0.01 to 1.0 part by mole of V₂O₅.
 3. Thedielectric ceramic composition according to claim 1, further comprising0.2 to 1.0 part by mole of Al₂O₃ and/or B₂O₃.
 4. The dielectric ceramiccomposition according to claim 2, further comprising 0.2 to 1.0 part bymole of Al₂O₃ and/or B₂O₃.
 5. A multilayer ceramic capacitor comprisinga laminated structure of a ceramic dielectric and an electrode; whereinthe ceramic dielectric is made of a dielectric ceramic composition asset forth in claim 1; and wherein the electrode is made of Ni or analloy containing Ni.
 6. An electronic component including a portion madeof the dielectric ceramic composition as set forth in claim 1.